In the United States the vast majority of crops are planted with row crop planters, grain drills or air seeders. Row crop planters are designed to place seeds in rows far enough apart to permit the control of weeds by cultivation and to improve harvesting efficiency. Grain drills and air seeders are used in solid planting, when row spacing is too close to permit cultivating or other cultural practices.
All three seeding machines, meter seed so it can be planted uniformly in a field. The row crop planters usually have the more sophisticated metering equipment for singling seeds, whereas the drills and air seeders use volumetric meters which apply a fixed volume of seed per linear foot. Volumetric meters typically comprise fluted drums which rotate through the seed reservoir, as illustrated in U.S. Pat. Nos. 3,489,321 and 3,763,797. Of particular interest is U.S. Pat. No. 3,489,321 which discloses a metering drum having helical flutes.
Singling mechanical seed meters used on planters include seed plate meters, finger pickup meters and “brush meters”. A seed plate seed meter is a mechanical seed meter having a rotating plate located at the bottom of the seed hopper. The plate is provided with seed cells in which the seed is trapped. If the cells are the correct size, only one seed will be trapped in each cell. The plate is then rotated over the discharge area and the seed released. U.S. Pat. Nos. 3,486,659, 4,282,985, and 4,609,131 disclose various configurations for seed plate type seed meters. Of particular interest is U.S. Pat. No. 4,609,131 which is a hybrid seed dispensing device also having a fluted drum for dispensing seed volumetrically.
Another mechanical seed meter is the finger pickup seed meter. This meter is used for corn and comprises a series of fingers that pass through the seed reservoir. The fingers are initially open in the seed reservoir and then close trapping seed between the fingers and a stationary plate. Additional seed trapped by the fingers is removed by passing the fingers over indentations in the stationary plate as the seed is transported to the discharge area where the finger is opened releasing the seed. One example of a finger pickup meter is disclosed in U.S. Pat. No. 3,552,601
Recently “brush meters” have been used for metering soybeans. A vertical rotating seed plate having a plurality of seed cells around its periphery passes through the seed reservoir. Seed is trapped in the seed cells by brushes. Examples of “brush meters” are disclosed in U.S. Pat. Nos. 4,924,786, 5,027,725 and 5,058,766.